Catalyst



-ZISheets-Sheet 1 Y U r Lo hrt .im U v An dJ n 'c 6` @MATT-.

Sept. 28, 1943. R. AUCHTER cATALYsT FiledA June 4, 1938 spfVn 28,1943..

R. AuczHTERA CATALYST Filed June 4, 1938 2 Sheets-Sheet 2- l 'guiu7713752215011' Fuacmdf Auch-3er Patented 2,330,539 caranrs'r RulandAuchter, Konigsbach in Baden, Germany: vested in the Alien PropertyCustodian Application June 4, 193s. serial No. l211,739

- In June 7, 1937 4 Claims. (Cl. 252-434) The present invention relatesto catalysts conof thin wires woven into fine mesh gauzes or the like. A

Catalysts of this type are known in the art as useful for the catalyticoxidation oi ammonia to nitric acid and lior similar .purposes asdescribed for instance in U. S. Patent No. 1,978,198.l

It has been observed that practically all of the catalytic materialssuitable for the purposes v taining platinum or platinum alloys in theform ual reduction ofthe catalytic eiiiciency owing to the increasingloss of catalytic material.

Applicant found further, that. in a catalyst having several layersconnected nrmly together by heat merged bonds, the disintegration of anouter layer oi' a materiall that. is easilystarted and has arelativelysmall maximum lefdciency,

, will proceed only very slowly beyond the maximentioned are, indifferent degrees, subject to a-y gradual mechanical disintegrationcaused by the chemical reaction which occurs owing to the` presence ofthe catalysts. As a consequence of this disintegration which proceedsfrom the outer surface towards the coreof the catalyst wires, during anextended period of use of the catalyst,

a very considerable loss of precious metal takes place and results in agradual reduction and eventually in a complete cessation of catalyticactivity. i

Some alloys combine with a relatively high catalytic efficiency arelatively great resistance to v mechanical disintegration.However-.these latter alloys are diillcult to start.

One object ofthe present invention is to produce a catalyst which'iseasily started, but oil'ers a high resistance to mechanicaldisintegration so that the loss of precious metal is' considerablysmaller and the length of time during which the catalyst operatesefiiciently is substantially greater thanwith the catalysts usedheretofore.

of such outer layer'is 'attained and are at .thisdepth iirmly connectedby heat merged bonds toj Ithe outermost crystals oi an inner layer arepar mum eiliciency stage, i! the innermost crystals of such outer layerare bonded at the depth where\ 'l `the maximum eillciency of the outerlayer is atg tained, to the outermost crystals ,of an-.inner layerhaving la greater resistance against disin-y tegration and a highercatalytieeiliciency and being less easily started. Moreover, theinnermost crystals of an outer layerwhich are disposed at the depthwhere the maximum elciency ticularly adapted and capable yoistarting thecatalytic activity of such inner layer.

Based onlthese discoveries. the a'bove mentioned objects areaccomplished by vthe new catu alysts set forth in the followingdescription, deilned inthe appended claims andA Illustrativelyexemplified in the accompanying drawings in Another object of theinvention is to produce a multi-layer catalyst which is easily startedand .reaches its maximum elciency inra very short time.

Still another object oi' the invention is to produce a multi-layercatalyst which is easy to be started and has a high maximum eillciencyand in which all of' the layers remain catalytically active during theentire reaction period oi' the catalyst.

A still further object of the invention is to provide a multi-layercatalyst in which each outer layer is of a kind to more easily initiatea chemical reaction than the next following inner layer and serves tospeed up the activation or the latter which in turn has a highercatalytic eihciency.

Applicant found that each catalytic material reaches its maximumeillciency, when the loosening of the crystals has proceeded from theouter surface to a certain depth, while further disintegration does notbring about any increase of eiliciency, but, on the contrary, results ina gradwhich Fig. 1 is a cross-section throughs catalyst i a nrstembodiment o! the inl wire according to vention.

Fig. 2 is a cross-section of a catalyst wire according to a secondembodiment of the invention.

. Fig. 3 is a longitudinal section of a multi-layer catalyst wire with adisintegrationcurve and a mechanical resistance curve being added.

Fig. 4 'is a cross-section through'v a multi-layer catalystioilconstructed according to the invention. l

Fia. 5 ,is a cross-sectional view of a catalyst wire composedof 24diil'erent sectors, illustrating and representing 23 examples o! catalyswire according to the inventiomand Fig. 5a is a key for Fig. 5.

Referring now'to the drawings and rst to Figure l, a denotes a metalliccore consisting of an alloy whichoilers a high resistance tofdisuintegration caused by catalytic reaction. The alloy from which thel coreis formed may have,

for instance. a highmeiting point which prevents it from beingchemically attacked at the ordinary working temperatures of thecatalytic reaction, or ity may contain a quantity of cata lyticallyinactive components. A casing c oiva catalytic metal, for instan-ceplatinum or a platinum alloy. which is easier to start than the alloyforming the core a, surrounds the latter.

The casing is applied to the core, for instance by galvanization andsubsequent forging at a high temperature preferably exceeding 1000 C. Itis also possible to Weld a thin metal sheet around the rough core and toroll theresulting multi-layer wire. Temperatures are used at which themetal of the casing is at least soft, up to temperatures where thismetal is in the liquid state. As a result of this heat treatment, thecrystals of the outer casing combine intimately with the crystals of thecore ina heat;

merged bond. Instead of one casing, severalcatalytically active casingsmay be applied one on top of the other in the manner described. Owing`to the heat merged bond, a diffusion of the outermost crystals of thecore a with the innermost crystals of the casing c takes place in the lzone b. .As a result, the casing c is anchored 'rmly on the core a andwill remain solidly supported by the core even after the crystals of theL casing have; become partly loosened.

Moreover, in contradistinction to` activating Y platinum layers whichhave been applied heretonot volatilize during the initial stages of thereaction and remains active during the entire service period of thecatalyst. On the other hand,

t, theintimate 4connection between the easily started` and highly activecasing c and the core a which is less easily started and has a greaterresistance against disintegration, causes at least a portion of rhodium,ruthenium, osmium, platinum, irldium, palladium, silicon, andchrome-nickel. Wherever per cent figures are inscribed into sector zonesin Fig. 5, it is to be understood that the layers represented by suchzones consist of an alloy of platinum with the element indicated by theshading, the latter being present in the percentage given.

The total diameter of a catalytic wire as represented by the' differentsectors of Fig. 5 may be 0.06 mm., but a core of 0.04 mm. diametergenerally does not participate in the catalytic action. According to theinvention, the catalytically active outer portion of the wire, which hasa thicknes of 0.01 mm., is divided into several concentric zones ofdiierent composition. If, as shown in Example 24, the catalyticallyactive wire portion is equally subdivided into iive con- ,the corefq tolparticipate in the catalytic action y of` thefcasing.

Fig. 2 illustrates a catalyst wire having an 'outer peripheral surfaceVa` and a core and several catalytic casings surrounding the core and Yone another'and merging into'one 'another on lines c and d. In thecourse`of "a reaction period, the outermost casing between lines a, and

b is iirst started. When the crystals oi' this layer adjacent line bhave become activated, the second casing between lines b and c is drawninto the reaction. `As the reaction proceeds, the latter casing, inturn,`activates the third casing between c and d and so on, each innercasing consists of a catalytic material more difficult to start and ofgreater maximum catalytic efficiency and greater resistance todeterioration than the next l following outer layer, but the core may bemade from a material which is catalytically inactive.

According to Fig. 3, a catalytically inactive core a having an outersurface his enclosed in anchored on -and supported by the core a.

i Fig. 4 illustrates a laminated catalytic foil having a. central layera. covered on opposite surfaces with successive catalytic layers l)I andd,

The shaded sectors of Fig.- 5 illustratedifferent examples,respectively, of catalytic wire con'- structed according to theinvention. As indicated by the key Fig. 5a the different shadingsindicate the presence of the following materials:

loosenedy the Whole laminated structure is rmly l centric zones, eachzone will have a thickness of 0.002 mm.

Sectors I to 3 of Fig. 5 illustratively exemplify catalyst wires for.use in reactions carriedout at relatively low temperatures up to 680.

The wire according to Example i comprises an outermost layer having athickness of 0.002 mm. and consisting ,of va. platinum alloy containing3% rhodium. This layer, owing to its lowl rhodium content, is easilystarted, but subject to a relatively rapid disintegration. In the nextiollowing layer which has a thickness of V0.004 mm., the rhodiumvcontent of the platinum alloy is increased to.5%. This second layerhasa correspondingly higher resistance to disintegration and islesseasily started than the outermost layer, The third layer is 0.004mm. thick and contains 7.5% rhodium and the core consists of a platinumalloy containing 10% rhodium.

The third layer oiers a very considerable resistance to catalytic`activation and disintegration and the core is practically catalyticallyinactive.

In Example 2, the outermost layer has the same thickness and compositionas in Example 1, but the next following layer is 0.006 mm. thick andconsists Aor a platinum alloy containing 3% ruthenium, .while the corehas a diameter of 0.044 mm. and consists of an alloy of platinum with 5%ruthenium.

According to Example 3 anoutermost layer of 0.002 mm. thickness consistsof pure platinum and serves to excite a core of 0.056 mm. diameterconsisting of a platinum alloy containing 3% ,rutheniurm Examples 4 to12 illustrate catalyst wires adapted for reactions carried out attemperatures between 680 C. and 780 C.

A catalyst Wire according to Example 4 comprises a core having adiameter of 0.04 mm. The core consists of a platinum alloy containing15% rhodium and having a high reaction resistance and a high meltingpoint. An outer casing having a thickness of 0.01 mm. and consisting ofa platinum alloy containing 5% rhodium surrounds thevcore and'isconnected thereto by heat merged bonds. A catalyst wire netfmade withwire of this type and used in an ammonia converting plant reached itsmaximum yield after 14 days"service.`

Inthe wire according to Example 5, the core also contains '15% rhodium,butin this case its diameter is 0.056-mm., while the thickness of theouter casing consisting of a` platinum alloy conis 0.002, mm.

afterhaving been started by the this layer contains lowinglayer is 0.004mln. a platinum alloy with '7.5% core has a diameter of, a platinumalloy containing rhodium.

rhodium, While the The wire of Example 7 has an outer layer of 0.002 mm.thickness:l 'This layer consists of platinum alloyed with 5% rhodium andmerging directly into the surface of a core of 0.056 mm. diameterconsisting of a platinum alloy containing 8% ruthenium.

Each of Examples 8 to 12 refers to a catalyst wire having an outermostlayer of the same dimensions and composition as that of the wire ofExample 7.

However, according to Example 8 a second layer, which is 0.004 mm. thickconsistsof platinum alloyed with 3% iridium and a core of 0.048 mm.diameter consists of a platinum alloy with 7% iridium In the wire ofExample 9, the second layer and the core have the same dimensions as inExample 8, but the second layer consists of platinum alloyed with 7.5%rhodium and the core consists of a platinum alloy containing 3%'ruthenium and 3% iridium.

In Examples 10, 11 and 12 the thickness of the second layer is only0.002 mm. and this layer consists of platinum alloyed with '7.5%rhodium. In each of Examples 10 to 12 the core has a diameter of 0.052mm. l

According to Example 10 the core consists of a platinum alloy containing6% silicon, according to Example 11 the core consists of platinumalloyed with 3% silicon, and 3% iridium and in 0.048 mm. and is made of4Examples 123s and 24 show outercasingof pure platinumyseveralintermedie metal alloys as for instance chrome-nichel. As

vindicated in Example" 16, .undercertain. circum-A "Y- stances; thecorevmay-` bemadefrom achromenickel'alloy containingiron.v t. wires,comprising an at'e'- reaction layers consisting.v of platinumalloys freeyof-rh`odium anda coreconsistingpa non- --"p'recious xnetalalloy... e tv.

I claim:

1. An active platinum catalyst comprising a wire gauze, each of thewires of said gauze comprising a plurality of layers of material, thelayer of material next adjacent the surface comprising 4a. catalyticallyactive platinum alloy of crystalline structure and the outer layercomprising a material selected from the group consisting of plat-Example 12 the platinum alloy of the core cony relatively heavy duty inammonia converting plants operating at high temperatures.

Example 13 shows a wire comprising a core and three successive casingsall consisting of platinum rhodium alloys, the rhodium content in thealloy of the outermost casing being 10% and increasing graduallyinwardly.

Example 14 refers to a wire having four reaction casings consisting ofplatinum rhodium alloys, the rhodium content of the alloy of each innercasing being greater than that of the alloy in the next following outercasing. Each casing is 0.002 mm. thick and the innermost casing ismounted on a core of 0.048 mm. diameter Aand consisting of a platinumalloy containing 8% iridium.

Examples 15 and 16 refer tomulti-layen'wires in which the differentlayers contain a low percentage of rhodium or no rhodium at all and theproper inwardly increasing resistance to disintegration is attained byusing suitable alloys of platinum with other metals such as rutheniumand osmium.

Examples 17 and 18 refer to wires without rhodium. In these cases inner.layers containing platinum alloys free of rhodium and having aninwardly increasing resistance against disintegration are excited byouter casings consisting of pure platinum.

According to Examples 19 to 21 reaction cas-` ings of diiierent platinumrhodium alloys are combined with cores consisting of non-precious inumand the platinum alloys which initiate chemical reactions more easilyand have less re'- sistance to disintegration than the platinum alloy ofsaid inner layer, the outer layer being of such thickness that theinnermost crystals of said outer layer are disposed at a depth to whichthe reaction penetrates and the crystals of the outer layer are loosenedwhen the catalyst has been initially activated to a maximum eiliciency,said innermost crystals and the outermost crystals of the rst mentionedlayer being interlaced and connected by heat merged bonds with theoutermost crystals of said inner layer so that after the catalyst hasbeen activated the crystals of the outermost layer will be supported bythe 'crystals of the inner layer.

2. An active platinum catalyst wire comprising an inner circumferentiallayer of a catalytically active platinum alloy of crystalline structure,and an outer circumferential layer of a crystalline catalytic materialselected from the group consisting of platinum and the platinum alloyswhich are more easily activated and have a smaller resistance todisintegration than the platinum alloy of said inner layer, said outerlayer having a thiclmess of the order of .002 mm. and having been heatmerged with the inner layer at a temperature exceeding 1000 degrees C.and below the melting point of said outer layer so that a bond isproduced between said inner and outer layers capable of inhibiting lossof said outer layer after activation and consequent loosening of thecrystals thereof.

3. A composite platinum rhodium catalyst wire comprising a laminatedmass of several successive circumferential layers, the outerlayercomprising f a crystalline catalytic material selected from the groupconsisting of platinum and platinum-rhodium alloys containing a minorproportion of rhodium, each successive layer towards the center of saidlaminated mass having a', relativelylarge proportion of rhodiumvascompared to each layer immediately outward therefrom so that outerlayers of said mass will be more easily activated and the inner layersof said mass will be more resistant to disintegration, all of the layersof said mass having been homogeneously heat merged by forging afterassembly at temperatures above 1000 degrees C. and below the meltingpoint thereof.

4. An active platinum catalyst wire comprising a plurality ofcircumferential layers of material, the layer of materialnext adjacentthe surface comprising a catalytically active platinum alloy ofcrystalline structure and the outer layer comprising a material selectedfrom the group con'- sisting of platinum and the platinum alloys whichlinitiate chemical reactions more easily and have less resistancetodisintegration than the platinum alloy of said inner layer, the outerlayer being of :such thickness that the innermost crystals of said outerlayer are disposed at a depth to which the reaction penetrates and thecrystals of the out'er llayer are loosened when the catalyst'has beeninitially activated to a. maximum efilciency, said innermost crystalsand the outermost crystals of the rst mentioned layer being interlacedand connected by heat merged bonds with the outermost crystals of' saidinner layer so that after the catalyst has been activated the crystalsof the outermost layer will be supported by the crystals of the innerlayer.

RULAND AUCH'I'ER.

